Anode current regulation



Feb. 7, 1961 Y P. J. ERDLE 2,971,160

ANODE CURRENT REGULATION Filed Nov. 25, 1958 .9a gf 96 ATTORNEY United States Patent @hice 2,971,160 Patented Feb. 7, 1961 AN ODE `CURRENT REGULATION Paul J. Erdle, Prospect Park, Pa., assignor, by mesne assignments, to Sylvania Electric Products Inc., Wilmington, Del., a corporation of Delaware Filed Nov. 25, '1958, Ser. No. 776,224

7 Claims. (Cl. S30-65) This invention relates to electron tube structure and circuitry involving said tube wherein a resistance element having positive coeficient of resistance characteristics used in the tube circuit is in heat conductive relationship with one of the electrodes in the tube.

In many uses of a tube it is desirable to utilize resistors connected with the electrodes within the tube to control the voltage applied tothe tube, for example, a resistor in the cathode circuit to control the biasof a control grid, or a resistor in the screen grid circuit to ldrop the screen grid voltage below that of the anode. In normal circuitry these and other resistors would be resistors having lineal resistance characteristics with heat and would be outside of the envelope whereby the heat created by the resistors would be dissipated.

lt is an objectl of this invention to thermally couple one or more resistors whether without or within the envelope of an electron tube with electrode elements within the envelope so that the heat generated by the resistor or resistors contributes to the proper functioning of the electron tube, the resistor or resistances being in the tube circuit and at least one of them being of the positive coeficient of resistance type.

lt is a more specific object of the invention to place the said resistor or resistances within the tube envelope and close to one of the electrodes to better afford tube current regulating functions.

These and other objects will become apparent upon consideration of the following specification when taken in association with the accompanying drawing in which:

Fig. l, in diagrammatic form, shows the resistor as part of a screen grid circuit and in close heat conductive relationship with an anode.

Fig. 2 is a modification of the structure of Fig. 1 wherein the screen connected resistor is in close heat conductive relationship with the cathode.

Fig. 3 is a modification wherein an anode connected resistor is in heat conductive relationship with the cathode and Fig. 4 is a modification wherein a cathode connected resistor is in heat conductive relationship with the cathode.

In Fig. 1 of said drawing there is diagrammatically illustrated a stage in an electron tube circuit, for example, the final amplifier of a transmitter employing a type 813 tube. The tube comprises an evacuated envelope containing therein a filamentary cathode 12, a control grid 14, screen grid 16, suppressor grid 18 and carbon anode 20. In addition to these elements, in accordance with the invention, there is inserted, preferably within the tube and in close proximity to the anode, a metal casing 22 which may be of cyindrical form insulated interiorly with a coating 24 of aluminum oxide and housing a resistor 26 which has a positive coefficient of resistance with heat. That is to say, as the temperature of the resistor rises, its resistance also increases. The resistor is embedded tightly within the casing to permit of ready transfer of heat therebetween. The casing 22 and anode 20 are inter-connected by a heavy metallic strap 28 so that heat from the anode may be transferred to the casing and resistor. Because in a beam power tube or pentode an increase of plate current is accompanied by an increase of screen current and vice versa, any tendency of plate current to rise in the tube causes a greater heating of the resistor 26 both by screen grid current increase and by greater heat transfer from the plate, thereby tending to increase the resistance of the screen resistor 26 and thereby tending to reduce the screen voltage and plate current. Thus by proper choice of screen grid resistance any desired regulating function may be obtained. An excess amount of screen voltage dropping resistance Within the tube may be avoided by placing part of the resistance external of the tube as indicated at 30 and 32, and the resistance 32 may be made variable to attain any desired regulatory characteristic of the part of the resistance within the tube.

In the modification disclosed in Fig. 2, wherein the tube is adapted to be placed in the same circuit as in Fig. l, the screen grid voltage dropping resistor of positive coeflicient of resistance is shown in heat conductive relationship with the cathode 12, this being effected by welding a bar 34 to the casing 22 and to the upper end of filamentary cathode 12, or to the upper end of a cathode sleeve in the case of an indirectly heated cathode. As the resistance of the resistor 26 increases due to increased screen grid current, and therefore increased plate current, the resistor current will be caused to diminish, thereby imparting less heat to the cathode, thus allowing its temperature to fall, become less emissive, and reduce the electron conduction of the tube. It will therefore be seen that the resistor in addition to supplying part of the heat necessary to maintain cathode heating also exercises a current regulatory effect on the tube.

In the modification show in Fig. 3 there is disclosed a triode having an anode 40, control grid 42 and cathode 44. The grid is fed with signals via a capacitor 46 bypassed with a grid leak resistor 48, and a biasing potentiometer 50 is connected to thegrid, all as: conventional in the art. The cathode is of the indirectly heated type and comprises a grounded emissively coated cathode sleeve 52 within which is a heater 54 connected to a suitable low voltage current supply. The heater coil by itself is insucient to maintain the` proper operating temperature of the cathode sleeve and is assisted by another heater in the form of a resistor 56 having a positive coefficient of resistance, said resistor being grounded at one end and connected at its other end via series connected potentiometer 58, outside of the tube envelope, high voltage direct current supply 60' and the primary of an output transformer 62 to the tube anode 40'. As the plate current tends to rise, the resistance of the resistor 56 increases thereby tending to diminish the cathode temperature and the electron emission from the cathode. Thus the current iiow will be stabilized.

The regulatory effect of the resistor 56 can be controlled by judicious choice of resistor and by adjustment of the potentiometer so that .j the resistor changes will have but insignificant effect upon normal rapid signal changes applied to the control grid but to become effective upon abnormal conditions. Upon changes in current, the normal heat reservoir provided by the cathode assembly retards electron emission readjustment and such readjustrnent will not take place unless the current change persists for a prolonged period of time.

In Fig. 4 there is illustrated a conventional output stage of an audio amplifier involving an electron tube having anode 70, control grid 80 and cathode 9i). The cathode is of the indirectly heated type and comprises an emissively coated cathode sleeve 92 heated by an internal heater 94 connected to a source of energy. Also within the sleeve is the grid bias resistor 96 connected in Series with the sleeve and ground, the grid resistor 98 of the resistance coupled network to the previous audio stage also being grounded. The resistor 96 will function to regulate the tube anode current much the same as in the previous cases.

In all of the modifications, it will be noted, the current tio-W through a resistor ywhich conventionally is outside of the electron tube not only functions in its normal capacity in the circuit, but also functions to have a regulatory effect upon the anode current by being placed in heat conductive relationship with an electrode, and by, preferably, being placed within the envelope in close relationship with said electrode.

Having thus described the invention what is claimed is:

1. An electron tube having electrodes comprising a cathode and an anode, a control grid, an input circuit connected to the grid, an output circuit connected to the anode, and a resistor in one of the circuits, said resistor having a positive coethcient of resistance and located within the tube in thermal contact with one of the electrodes to exert a regulatory effect upon the anode current.

2. An electron tube having electrodes comprising av cathode and an anode, a control grid, an input circuit connected to the gn'd, an output circuit connected to the anode, and a series resistor in one of the circuits, said resistor having a positive coefiicient of resistance and 1ocated Within the tube and in good heat conductive relationship with one of the electrodes to exert a regulatory effect upon the anode current.

3. An electron tube having a cathode, control grid, screen grid and anode, an input circuit to the control grid, an output circuit, a direct current source of supply connected to the anode, a resistor having a positive coeicient of resistance in Series with said screen grid and said source of supply, said resistor being located within the envelope and in thermal contact with the anode.

4. An electron tube having a cathode sleeve, control 4 grid, screen grid and anode, a resistor having a positive coefficient of resistance Within the sleeve in heat transfer relationship thereto and a circuit placing the resistor in series with the screen grid.

5. An electron tube having an indirectly heated cathode sleeve with means to heat the saine, a control grid and an anode, an extra heating element within the sleeve in heat transfer relationship therewith, said element having a positive coeticient of resistance and circuit means connecting said extra heating element with said anode.

6. An electron tube having a cathode sleeve With an electron emissive surface, a heater Within said sleeve, a second heater within said sleeve which has a positive coecient of resistance in heat transfer relationship to the sleeve, said tube also having a control grid and an anode, and circuit means connecting the second heater with said cathode sleeve.

7. An electron tube having electrodes comprising a cathode assembly including a cathode sleeve; and also an anode, a control grid, an input circuit connected to the grid, an output circuit connected to the anode, a heater formingpart of the cathode assembly, and a resistor in one of the circuits, said resistor having a positive cofficient of resistance and located within the cathode sleeve and in heat conductive relationship With the sleeve to exert a regulatory effect upon the anode current.

References Cited in the file of this patent UNITED STATES PATENTS 1,675,334 Donle July 3, 1928 1,998,199 Mavrogenis Apr. 16, 1935 2,144,509 Renatus Ian. 17, 1939 2,247,198 Krefft June 24, 1941 2,668,930 Suits Feb. 9, 1954 2,813,227 Sweet Nov. 12, 1957 2,875,377 Woo Feb. 24, 1959 

